Numerical investigation of ship-induced drawdown waves in confined waters

During navigation, ships generate both long-period primary waves and short-period secondary waves, which can transfer energy to canal boundaries and thereby disturb aquatic ecosystems and alter shoreline morphology. Despite increasing interest in ship hydrodynamics, existing numerical models remain ship-centred and pay limited attention to ship-induced environmental impacts. In this study, one of the main components of the primary wave system, drawdown wave and its impact to the canal boundaries were investigated. Unsteady Reynolds-averaged Navier–Stokes simulations were carried out using Computational Fluid Dynamics software for a 1:75 scale KCS ship model under different confinement conditions and depth Froude numbers. Comparisons with available empirical and analytical models indicate that these approaches generally underestimate drawdown relative to CFD predictions. Spatial Fast Fourier Transform of the wave profiles further showed that the dominant drawdown components are characterised by dimensionless wavenumber ( kh ) below 0.3, which correspond to wavelengths greater than two ship lengths. Meanwhile, the FFT–IFFT reconstruction effectively separated the primary drawdown wave from the secondary wave system. The results indicate that both canal confinement and vessel speed are strongly associated with the magnitude of drawdown and the resulting hydrodynamic loads acting on the canal boundaries. The study demonstrates the capability of CFD to support the assessment of ship-induced environmental impacts in confined waterways.